(a) Field of the Invention
The present invention relates to a series battery charger, and more particularly to a charger designed for charging, discharging and supplying electric power to an AA or AAA rechargeable battery, and a synchronous changeover switch module is provided to integrate a circuit structure with “a separate detection charging circuit and a series combined discharging circuit”.
(b) Description of the Related Art
As portable 3C electronic products become increasingly more popular, the demand for batteries becomes increasingly higher as well. A disposable battery (or a primary battery) is discarded after use, not only increasing the cost, but also causing environmental pollutions. Therefore, a rechargeable battery (or a secondary battery) has a higher consumption than that of the primary battery since the rechargeable battery can save costs and reduce contaminations of waste batteries.
At present, the rechargeable battery includes lithium-ion (Li-ion) battery, nickel metal hydride (Ni-MH) battery, nickel cadmium (Ni—Cd) battery and the rechargeable alkaline battery, and these batteries are also known as secondary batteries. Recently, a lithium battery with an organic electrolytic unit is used extensively in portable electronic devices due to its features of high-capacity density, low temperature, and stable storage.
However, the lithium battery still has the following drawbacks in its use:
1. The lithium battery usually comes with a different specification for each of the electronic products. Even for the electronic products of the same brand, such as the Nokia mobile phones, there are tens of models of the lithium batteries, and thus causing tremendous inconvenience and trouble to users.
2. The lithium battery contains an electrolytic unit, and there is a safety concern such as possible explosion occurred when a current is passed.
3. Most of the present portable powers use a built-in lithium battery as an energy storage unit, but it generally does not come with a standard size for general electronic consumer products. As a result, the fully charged battery cannot be used alone when it is removed. Even though it can be removed, there are so many specifications of the lithium batteries, and such application is impractical.
Compared with the lithium battery, although the secondary battery such as the nickel metal hydride (Ni-MH), nickel cadmium (Ni—Cd) or alkaline rechargeable secondary battery has an energy storage density less than that of the lithium battery, yet its widely used AA or AAA battery sets an industrial specification, which is the main reason of its popularity up to now. However, its use still has the following insufficiencies:
1. As shown in FIG. 1, which illustrates a charging circuit of a conventional parallel charger, the batteries B1˜B4 connected in parallel are charged by the charging circuit. The advantage lies in that each of the batteries obtains a roughly the same charging voltage. The user can be free of the problem with batteries that are overcharged or undercharged. However, the disadvantage of the parallel charging mode is that the batteries can't be rapidly charged. Each of the batteries has only 1.2˜1.5V. When they are used/discharged for the 3C electronic products, they have to be connected in series for obtaining the DC voltage of (1.2V˜1.5V)×4=4.8V˜6V. It is complicated to discharge the parallel-connected batteries in a series way. Moreover, the problems such as power consumption, voltage difference and overheat have to be overcome.
2. As shown in FIG. 2, which illustrates a charging circuit of a conventional series charger, the batteries B1˜B4 connected in series are charged by the same charging circuit. The advantage is that the structure is simple and the batteries can be rapidly charged. However, this application may have drawbacks such as overheat, leak and undercharge.
3. In order to improve the above-mentioned charging circuit, the applicant of the invention disclosed a solution of U.S. Pat. No. 6,784,638 “Series Charger with Separate Detection of Batteries” with which a plurality of batteries connected in series can be charged. In addition, a control IC and a separate detection circuit are employed to conduct the detection control of each battery. In this way, the problems of the series charger and the parallel charger may be eliminated. By use of this series charger with separate detection of batteries, the batteries each can be charged and detected if they are fully charged. However, it is not possible as well to discharge the batteries in a series mode for the 3C electronic products. This requires further improvements.